A power system is constructed by connecting power generation equipment and load equipment by a power transmission facility. There are power systems in various scales from a large-scale system connecting a plurality of large-scale power plants and many factories, commercial facilities and households to a small-scale system constructed within a specific facility.
In-plant equipment provided in a plant such as a power plant or a factory includes, for example, a load system, a power generation system, and a storage battery system. The in-plant equipment is connected to a power system. The power system or the in-plant equipment includes an energy management system (EMS) that manages at least in-plant electric power supply/demand, and the electric power supply/demand of the individual systems and the power system is balanced by the energy management system.
One type of power generation system utilizes natural energy such as sunlight and wind power. The power generation system utilizing the natural energy is being widely introduced in response to rise in awareness of energy problems or environmental problems in recent years. However, the power generation system utilizing the natural energy has a disadvantage that power cannot be stably supplied since generated power tends to be controlled by natural factors such as seasons and weather. In order to make up for the disadvantage, the equipment for which the power generation system and the storage battery system are combined is being considered.
The storage battery system is used as a means for stabilizing power supplied to a load system by the power generation system and the power system, or power supplied to the power system and the load system by the power generation system. It was thought before that it is difficult to store a large amount of power, however, since a storage battery of a large capacity such as a lithium-ion battery and sodium-sulfur battery is put into practical use, it is made possible to store the large amount of power. By connecting the storage battery system including such a storage battery to the power generation system, an operation is possible in which excess power is charged in the storage battery when supply is excessive in contrast with power demand, and power insufficiency is compensated by discharge from the storage battery when the supply is insufficient in contrast with the power demand. By combining the storage battery system with the power generation system utilizing the natural energy, the generated power that fluctuates depending on seasons and weather or the like is leveled by charge/discharge of the storage battery, and the power can be stably supplied to the power system.
Note that the applicant recognizes literatures described below as the ones associated with the present invention. JP 2014-117003 A discloses a configuration that a photovoltaic power generation system and a storage battery system are connected and fluctuation of generated power of photovoltaic power generation is suppressed by charge/discharge control of a storage battery. JP 2014-124063 A discloses one example of the storage battery system including a plurality of power conditioning systems (PCSes) connected to the power system. JP 2012-43623 A discloses a configuration of calculating a charge rate of the storage battery from an integrated value of a current flowing to the storage battery.